On 10/23/24 08:05, Kevin Brodsky wrote:
...> diff --git a/tools/testing/selftests/mm/pkey-x86.h
b/tools/testing/selftests/mm/pkey-x86.h
> index 5f28e26a2511..53ed9a336ffe 100644
> --- a/tools/testing/selftests/mm/pkey-x86.h
> +++ b/tools/testing/selftests/mm/pkey-x86.h
> @@ -34,6 +34,8 @@
> #define PAGE_SIZE 4096
> #define MB (1<<20)
>
> +#define PKEY_ALLOW_NONE 0x55555555
Hi Kevin,
Looking at this in context, I think "PKEY_ALLOW_NONE" is not a great
name. On one hand, we have:
PKEY_DISABLE_ACCESS
PKEY_DISABLE_WRITE
which are values for *A* pkey.
But PKEY_ALLOW_NONE is a whole register value and spans permissions for
many keys. We don't want folks trying to do something like:
pkey_alloc(flags, PKEY_ALLOW_NONE);
If I were naming it in x86 code, I'd probably call it:
PKRU_ALLOW_NONE
or something.
> static inline void __page_o_noops(void)
> {
> /* 8-bytes of instruction * 512 bytes = 1 page */
> diff --git a/tools/testing/selftests/mm/pkey_sighandler_tests.c b/tools/testing/selftests/mm/pkey_sighandler_tests.c
> index a8088b645ad6..b5e1767ee5d9 100644
> --- a/tools/testing/selftests/mm/pkey_sighandler_tests.c
> +++ b/tools/testing/selftests/mm/pkey_sighandler_tests.c
> @@ -37,6 +37,8 @@ pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
> pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
> siginfo_t siginfo = {0};
>
> +static u64 pkey_reg_no_access;
Ideally, this would be a real const or a #define because it really is
static. Right? Or is there something dynamic about the ARM
implementation's value?
...
> * Setup alternate signal stack, which should be pkey_mprotect()ed by
> @@ -142,7 +145,8 @@ static void *thread_segv_maperr_ptr(void *ptr)
> syscall_raw(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0);
>
> /* Disable MPK 0. Only MPK 1 is enabled. */
> - __write_pkey_reg(0x55555551);
> + pkey_reg = set_pkey_bits(pkey_reg_no_access, 1, 0);
> + __write_pkey_reg(pkey_reg);
The existing magic numbers are not great, but could we do:
#define PKEY_ALLOW_ALL 0x0
So that this can be written like this:
pkey_reg = PKRU_ALLOW_NONE;
pkey_reg = set_pkey_bits(pkey_reg, 1, PKEY_ALLOW_ALL);
That would get rid of the magic '0'.
> /* Segfault */
> *bad = 1;
> @@ -240,6 +244,7 @@ static void test_sigsegv_handler_with_different_pkey_for_stack(void)
> int pkey;
> int parent_pid = 0;
> int child_pid = 0;
> + u64 pkey_reg;
>
> sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
>
> @@ -257,7 +262,9 @@ static void test_sigsegv_handler_with_different_pkey_for_stack(void)
> assert(stack != MAP_FAILED);
>
> /* Allow access to MPK 0 and MPK 1 */
> - __write_pkey_reg(0x55555550);
> + pkey_reg = set_pkey_bits(pkey_reg_no_access, 0, 0);
> + pkey_reg = set_pkey_bits(pkey_reg, 1, 0);
> + __write_pkey_reg(pkey_reg);
... and using the pattern from above, this is quite a bit more readable:
pkey_reg = PKRU_ALLOW_NONE;
pkey_reg = set_pkey_bits(pkey_reg, 0, PKEY_ALLOW_ALL);
pkey_reg = set_pkey_bits(pkey_reg, 1, PKEY_ALLOW_ALL);
...
> + /* Only allow X for MPK 0 and nothing for other keys */
> + pkey_reg_no_access = set_pkey_bits(PKEY_ALLOW_NONE, 0,
> + PKEY_DISABLE_ACCESS);
If the comment says "only allow X", then I'd expect the code to say:
pkey_reg_no_access = set_pkey_bits(PKEY_ALLOW_NONE, 0, PKEY_X);
... or something similar.
